In recent years, with respect to image-forming apparatuses for outputting high quality images, digital copying machines, laser printers and other apparatuses have been put on the market, and have been widely used. Such digital copying machines and laser printers are equipped with optical scanning devices for carrying out laser optical scan recording processes. The laser optical scan recording process is based on an image-recording system for forming an electrostatic latent image on an image-bearing body by using a scanning beam beam released from a light source.
Such an optical scanning device in an image-forming apparatus is provided with a laser light source for successively emitting a light image modulated based upon image information and various optical members for allowing the light image released from the laser light source to be focused on the image-bearing body so as to form an image, and these members are placed with a predetermined positional relationship being maintained with each other.
Moreover, in the recent office environment, with respect to the digital copying machine and the laser printer, there have been demands for miniaturization so as to reduce the installation space to a minimum. Along with the miniaturization of the image-forming apparatuses, the optical scanning device for carrying out a laser optical scan recording process has come to be placed in a limited space in a positional relationship with other constituent parts inside the image-forming apparatus.
For this reason, in order to keep the optical scanning device from interfering with installations of other constituent parts in the image-forming apparatus, an arrangement has been proposed in which the light path of the laser light from the laser light source to the surface of the image bearing body is reflected by a mirror so as to be bent.
For example, Japanese Laid-Open Patent Application No. 301074/1988 (Tokukaihei 63-301074 (published on Dec. 8, 1988) ) discloses a laser printer optical system explained as follows: In this laser printer system, the light path of the laser light is bent by installing three mirrors. This arrangement makes it possible to secure the light path length within a limited space, and consequently to miniaturize the optical scanning device.
Moreover, Japanese Laid-Open Patent Application No. 128603 (Tokukaihei 7-128603 (published on May, 19, 1995)) discloses a digital color copying machine having the following arrangement: In this digital copying machine, a plurality of optical scanning devices are aligned in parallel with each other. Then, in order to minimize the distance between the optical scanning devices aligned in parallel with each other, the optical scanning devices are placed longitudinally.
In general, the optical scanning device for carrying out a laser optical scan recording process is provided with a deflection device constituted by a polygon mirror and a driving motor for the polygon mirror so as to deflect the laser beam. The deflection device of this type is designed to rotate the polygon mirror at high speeds. Here, since a great load is applied to the rotary shaft of the driving motor, problems with this arrangement are that the service life of the driving motor is shortened and that looseness of the rotary shaft tends to give adverse effects on recording images.
Therefore, in particular, in the arrangement as disclosed in the above-mentioned Japanese Laid-Open Patent Application No. 128603 (Tokukaihei 7-128603) wherein the optical scanning devices are placed longitudinally, that is, the rotary shaft of the driving motor is placed horizontally with respect to the optical scanning device main body, since the load applied to the driving motor becomes extremely great, the above-mentioned problems are more likely to occur.
Moreover, in the arrangement as disclosed in the above-mentioned Japanese Laid-Open Patent Application No. 301074/1988 (Tokukaihei 63-301074) wherein the rotary shaft of the driving motor in the deflection device is placed vertically to the optical scanning device main body with the laser light path from the light source is placed in a bent state, the following problems arise. That is, in the case when a plurality of the light scanning devices having the above-mentioned arrangement are aligned and placed, the optical scanning device itself becomes bulky, and the distance between the light scanning devices also becomes longer, failing to miniaturize the image-forming apparatus.
In particular, in the recent tandem-type image-forming apparatus having the optical scanning device and the photosensitive body aligned in parallel with each other, in order to reduce the installation area of the image-forming apparatus to a minimum, an arrangement is adopted in which small-size image-forming sections, which use a photosensitive body of 30 to 40 mm in diameter based on the electrophotographing process, are aligned in parallel with each other. Even if the small-size image-forming section is adopted in this manner, it is not possible to minimize the size of the image-forming apparatus itself, unless the size of the optical scanning device itself is made smaller.
Moreover, in the optical scanning device, each reflection mirror serving as an optical member for directing a laser beam from the light source to the surface of an image-bearing body is supported on a side face or the like of a support body by means of a securing member. However, due to distortion in the support body caused by insufficient strength of the support body, it tends to become difficult to accurately maintain the positional precision of the reflection mirror, causing an offset in the laser beam light path, with the result that it becomes difficult to form an electrostatic latent image accurately on the image-bearing body based upon image information.